Exploration of the ionizable metal cluster-electrode surface analogy: infrared spectroelectrochemistry of [Pt24(CO)30]N, [Pt26(CO)32]N, and [Pt38(CO)44]N (n = 0 to -10) and comparisons with potential-dependent spectra of carbon monoxide adlayers on platinum surfaces

Abstract

Infrared spectroelectrochemistry has been utilized to explore the vibrational properties of the high-nuclearity platinum carbonyl clusters [PtM(CO)3o]", [Pt26(CO)32]", and [Pt38(CO)44]" as a function of the charge n in dichloromethane, acetonitrile, acetone, tetrahydrofuran, and methanol. The clusters exhibit unusually reversible voltammetric and spectroelectrochemical behavior, with a sequence of redox steps spanning = 0 to (in one case) -10, having formal potentials, E¡, between ca. 0.5 and -2.5 V vs ferrocenium-ferrocene. Largely two-electron steps are observed for [Pt26(CO)32]", involving even-charge states ( = -2, -4, -6, -8, -10). Sequential one-electron steps are found for [Pt24(CO)30]" and [Pt38(CO)44]", although the regions of electrode potential over which odd-charge states (n = -1, -3, -5, -7) are stable (i.e., the spacings between E( values) are markedly smaller than those for the even-charge states. The C-O stretching frequencies for the bridging (veo) and especially the terminal (v'co) coordinated CO ligands decrease systematically as n becomes more negative; for example, t>c0 for [Pt24(CO)30]" diminishes by 15-20 cm-1 per added electron. The observation of such remarkable charge-dependent spectral properties for these large and structurally well-defined platinum clusters invites comparisons with the potential (and consequent charge)-dependent properties of CO adlayers at corresponding platinum electrode-solution interfaces. The latter systems also display decreases in veo and veo as the electrode potential, E, and hence the surface charge is made more negative, as usually ascribed either to increased dir(Pt) -* ir*(CO) backbonding or to a Stark effect. The vlco-E slopes for saturated CO adlayers at both single-crystal and polycrystalline Pt-nonaqueous interfaces are noticeably smaller than for the corresponding solvated Pt carbonyl clusters, the latter being adjudged from the vco~£f behavior. These differences are due chiefly to larger "effective surface" capacitances (i.e., charge-£f dependencies) for the clusters than those measured for the electrode-solution interfaces. Such differing capacitances can largely be accounted for by a simple geometric electrostatic model. When the ylco values are plotted versus the electronic charge per surface Pt atom ("surface charge density"), however, an essentially uniform y'co-charge dependence is observed for the different Pt clusters, with similar behavior being obtained for the Pt electrodes. These comparisons provide an intriguing link between the electronic and bonding properties of such large ionizable metal clusters with those of chargeable metal surfaces.

Synergic Binding of Carbon Monoxide and Cyanide to the FeMo Cofactor of Nitrogenase: Relic Chemistry of an Ancient Enzyme?

“…[24] As expected, the n( 12 CO) bands are shifted on isotopic 13 CO substitution by 44 cm À1 (Figure 6b). Although less intense and less well defined, it is apparent that the n(CN) bands are also shifted (by about 20 cm À1 ) upon 13 CO substitution.…”

Creation of active water-splitting photocatalysts by controlling cocatalysts using atomically precise metal nanoclusters

“…as protective ligands. [126][127][128][129][130][131][132][133][134][135][136][137][138][139][140][141][142][143] Furthermore, previous studies have demonstrated that size-controlled metal NCs can be loaded on a support by adsorbing such precise metal NCs on the support and then removing the protective ligands by calcination ( Figure 3C). [144][145][146]…”

Using EPR to follow reversible dihydrogen addition to paramagnetic clusters of high hydride count: [Rh6(PCy3)6H12]+and [Rh6(PCy3)6H14]+

“…[12][13][14][15][16][17] For example [W 6 CCl 18 ] n-(n = 0 to 4), 18 [W 6 NCl 18 ] n-(n = 1 to 3), 19 [FeS 8 (PEt 3 ) 6 ] n+ (n = 0 to 4) 20 and [Mo 6 S 8 (PEt 3 ) 6 ] n (n = 1+ to 2-) 21 have been described; while the hexanuclear cluster compounds with edge bridged halide ligands also exhibit extensive redox behaviour, 22-24 and redox pairs such as [Ta 6 Cl 14 (PEt 3 ) 4 ] n+ (n = 0, 1) have been isolated. 25 Up to ten sequential reversible reductions have been reported for the high-nuclearity platinum cluster [Pt 26 (CO) 32 ] n (n = 0 to -10). 26 EPR measurements have also been reported for a variety of medium and high-nuclearity clusters.…”

“…25 Up to ten sequential reversible reductions have been reported for the high-nuclearity platinum cluster [Pt 26 (CO) 32 ] n (n = 0 to -10). 26 EPR measurements have also been reported for a variety of medium and high-nuclearity clusters. [27][28][29][30][31][32][33] In the mono-metallic hydride arena, EPR studies on the redox pairs of 15 and 17-electron mono-nuclear hydrido 2+ .…”